DESCRIPTION (provided by candidate): This proposal will test the novel hypothesis that the auxiliary subunit NavB1 (SCN1b) plays a role in the regulation of native Kv4.2-encoded A-type potassium channels and, therefore, in the regulation of neuronal excitability. The hypothesis is based on biochemical studies that have unexpectedly shown that NavlJI co- immunoprecipitates with Kv4.2 from brain. Follow-up experiments in HEK-293 cells show that co-expression of Kv4.2 and Navfil increases potassium currents when compared to expression of Kv4.2 alone, demonstrating that NavlJI modulates the function of Kv4.2-encoded potassium channels in heterologous cells. Interestingly, a cysteine to tryptophan mutation (C121W) in SCN1b has been identified in patients with generalized epilepsy with febrile seizures plus (GEFS+) and in patients with temporal lobe epilepsy (TLE) and preliminary results show that coexpression of Kv4.2 with the C121W mutant in HEK-293 cells fails to increase Kv4.2-encoded potassium currents when compared to coexpression of Kv4.2 with wildtype NavS1. These results suggest that decreased A-type currents might contribute to increased neuronal excitability and epileptogenesis in GEFS+ and TLE patients. The experiments in this proposal will evaluate the physiological significance of the interaction of NavB1 (SCN1b) with Kv4.2. To this end, molecular genetic approaches to manipulate the expression of Nav&1 (as well as the expression of the C121W mutant) in vivo and in vitro will be used in combination with whole-cell voltage- and current-clamp recordings in both cultured cortical neurons and in cortical neurons in acute brain slices. The first specific aim will test the hypothesis that Nav&1 (SCN1b) modulates native Kv4.2-encoded A-type potassium currents and neuronal excitability and the second specific aim will test the hypothesis that expression of the C121W NavB1 mutant decreases native Kv4.2-encoded A-type potassium currents and increases neuronal excitability. The experiments described in this proposal will elucidate the physiological significance of NavB1 as a novel Kv4.2 auxiliary subunit that modulates native A-type potassium currents and neuronal excitability. Most importantly, the results from these experiments are expected to provide novel and potentially important insights into the mechanisms involved in the pathophysiology of generalized epilepsy with febrileseizures plus and temporal lobe epilepsy.